The present invention relates broadly to directional flow control or diversion valves, and more particularly to a valve of such type which is of spool-type variety and which is especially adapted for use in chemical-mechanical polishing (CMP) for controlling the supply of de-ionized water and slurry streams while allowing for constant recirculation of those streams.
In the general mass production of semiconductor devices, hundreds of identical xe2x80x9cintegratedxe2x80x9d circuit (IC) trace patterns are photolithographically imaged over several layers on a single semiconducting wafer which, in turn, is cut into hundreds of identical dies or chips. Within each of the die layers, the circuit traces are isolated from the next layer by an insulating material. Inasmuch as it is difficult to photolithographically image a rough surface, it is desirable that the insulating layers are provided as having a smooth surface topography or, as is termed in the vernacular, a high degree of planarity. In this regard, a relatively rough surface topography may be manifested as a depth of filed problem resulting in poor resolution of the patterns of subsequently deposited layers, and, in the extreme, in the short circuiting of the device. As circuit densities in semiconductor dies continue to increase, any such defects become unacceptable and may render the circuit either inoperable or lower its performance to less than optimal.
To achieve the relatively high degree of planarity required for the production of substantially defect free IC dies, a chemical-mechanical polishing (CMP) process is becoming increasingly popular. Such process involves chemically etching the wafer surface in combination with mechanical polishing or grinding. This combined chemical and mechanical action allows for the controlled removal of material.
In essential operation, CMP is accomplished by holding the semiconductor wafer against a rotating polishing surface, or otherwise moving the wafer relative to the polishing surface, under controlled conditions of temperature, pressure, and chemical composition. The polishing surface, which may be a planar pad formed of a relatively soft and porous material such as a blown polyurethane, is wetted with a chemically reactive and abrasive aqueous slurry. The aqueous slurry, which may be either acidic or basic, typically includes abrasive particles, a reactive chemical agent such as a transition metal chelated salt or an oxidizer, and adjuvants such as solvents, buffers, and passivating agents. Within the slurry, the salt or other agent provides the chemical etching action, with the abrasive particles, in cooperation with the polishing pad, providing the mechanical polishing action. The basic CMP process is further described in the following U.S. Pat. Nos.: 5,993,647; 5,928,492; 5,895,315; 5,855,792; 5,791,970; 5,755,614; 5,709,593; 5,707,274; 5,705,435; 5,700,383; 5,665,201; 5,664,990; 5,658,185; 5,655,954; 5,650,039; 5,645,682; 5,643,406; 5,643,053; 5,637,185; 5,618,227; 5,607,718; 5,607,341; 5,597,443; 5,407,526; 5,395,801; 5,314,843; 5,232,875; and 5,084,071.
Looking to FIG. 1, a representative CMP process and apparatus therefor are illustrated schematically at 10. The apparatus 10 includes a wafer carrier, 12, for holding a semiconductor wafer or other workpiece, 14. A soft, resilient pad, 16, is positioned between wafer carrier 12 and wafer 14, with the wafer being held against the pad by a partial vacuum, frictionally, or with an adhesive. Wafer carrier 12 is provided to be continuously rotated by a drive motor, 18, in the direction referenced at 20, and additionally may be reciprocated transversely in the directions referenced at 22. In this regard, the combined rotational and transverse movements of the wafer 14 are intended to reduce the variability in the material removal rate across the work surface 23 of the wafer 14.
Apparatus 10 additionally includes a platen, 24, which is rotated in the direction referenced at 26, and on which is mounted a polishing pad, 28. As compared to wafer 14, platen 24 is provided as having a relatively large surface area to accommodate the translational movement of the wafer on the carrier 12 across the surface of the polishing pad 28.
A supply tube, 30, is mounted above platen 26 to deliver a stream of polishing slurry, referenced at 32, which is dripped or otherwise metered onto the surface of pad 28 from a nozzle or other outlet, 34, of the tube 30. The slurry 32 may be gravity fed from a tank or reservoir (not shown), or otherwise pumped through supply tube 30. Alternatively, slurry 32 may be supplied from below platen 26 such that it flows upwardly through the underside of polishing pad 28. Large volumes of water, typically de-ionized, also must be supplied through tube 30 to rinse the slurry from the wafer, to clean the pad and platen, and to keep the polishing pad wet in between polishing cycles.
In addition to the supply of slurry and water to the polishing pad, the CMN apparatus must accommodate the recirculation of the slurry and water process streams. In this regard, if the slurry flow is not maintained between polishing cycles or during down time, the particles in the slurry can agglomerate which results in an undesirable condition. The water stream also may be recirculated during the polishing cycles.
Heretofore, various arrangements of separate valves and associated controls have been employed to provide the required flow control functions for the slurry and water streams. These arrangements, however, often are relatively complex, and may not be fully versatile in function and control. It therefore it is believed that improvements in the design of control valves for CMP process equipment would be well-received by the semiconductor manufacturing industry.
The present invention is directed, broadly, to directional flow control valves such as are described in U.S. Pat. Nos. 3,357,451; 3,742,981; 3,744,518; 3,744,522; 3,827,453; 3,854,499; 3,858,485; 4,022,425; 4,051,868; 4,167,197; 4,274,443; 4,294,287; 4,495,962; 4,526,201; 5,992,294; an in EP 879,979 and GB 2,199,115. More particularly, the invention is directed to a multi-port valve of such variety which is of a spool-type construction. In having a capability of selectively controlling the flow of two process streams without intermixing of the streams, and in having a further capability of accommodating flow-through recirculation of the streams in different operational modes, the valve of the present invention is especially adapted for use in control the flow of slurry and water streams used in CMP processes.
As utilized in the CMP process, the valve, which may be pneumatically, hydraulically, electromechanical, or manually piloted or actuated, is de-energized or otherwise positional in a null mode to recirculate the slurry and water streams. In a first operational mode, such as during polishing of the wafer, the valve is energizable or otherwise positional to deliver a portion of the slurry flow through a supply outlet while maintaining the recirculation flows. In an alternate second operational mode, such as for rinse or stand-by, the valve is energizable or otherwise positionable to deliver a portion of the slurry flow through a supply outlet while again maintaining the recirculation flows.
It therefore is a feature of a disclosed embodiment of the present invention to provide a valve for use within a fluid system having a first and a second fluid stream. The valve includes a body having a bore with first and second inlet and outlet port openings for the fluid streams, and a third outlet port opening selectably couplable with the first and second inlet ports. A spool or other valve element is slidably received within the bore for axial movement therein, and is positionable within the bore in a null orientation closing the third outlet port to the first and second inlet ports. The spool is movable from the null orientation to a first operating orientation opening the third outlet port path to the first inlet port, and to a second operating orientation opening the third outlet port to the second inlet port.
It is a further feature of a disclosed embodiment of the present invention to provide a method of controlling the flow of a slurry stream from a slurry reservoir and a water stream from a water reservoir in a chemical-mechanical polishing (CMP) system having a supply line for delivering the slurry and water streams to a polishing pad. The method involves providing a valve including a body having a bore with first and second inlet ports for the streams, first and second outlet ports coupled to the reservoirs, and a third outlet port coupled to the supply line of the system. A spool or other valve element is slidably received within the bore for axial movement therein, and is positionable within the bore in a null orientation closing the third outlet port to the first and second inlet ports. The spool is shiftable from the null orientation to a first operating orientation opening the third outlet port path to the first inlet port, and to a second operating orientation opening the third outlet port to the second inlet port.
The present invention, accordingly, comprises the apparatus possessing the construction, combination of elements, and arrangement of parts which are exemplified in the detailed disclosure to follow. Advantages of the invention includes a valve construction which is cable of selectively controlling the flow of two fluid streams to multiple outlets, and which is of a compact and efficient structure affording reliable operation. Additional advantages include a valve construction which is economical to manufacture and assemble, and which may be fabricated entirely of a thermoplastic or other polymeric material such as a fluoropolymer which is chemically-resistant and meets the rigorous service requirements specified in semiconductor manufacturing. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.